Electronic equipment using semiconductor devices are essential for many modern applications. Semiconductor image sensors are commonly involved in electronic equipment for sensing light. Complementary metal-oxide-semiconductor (CMOS) image sensors (CIS) are widely used in various applications, such as digital camera and mobile phone cameras. The CMOS image sensor typically includes an array of picture elements (pixels). Each pixel includes a photo-diode, a transistor or a capacitor. Electrical energy is induced in the photo-diode upon exposure to light. Each pixel generates electrons proportional to the amount of light falling on the pixel. The electrons are converted into a voltage signal in the pixel and further transformed into a digital signal.
CMOS image sensors are classified as front side illuminated (FSI) image sensors and back side illuminated (BSI) image sensors, depending on the light path difference. The BSI image sensors are gaining in popularity. The pixels in the BSI image sensor generate electrical signals in response to incident light. Magnitudes of the electrical signals depend on the intensity of the incident light received by the respective pixels. The light is incident on a back side of a substrate of the BSI image sensor and hits the photo-diode directly, without obstruction from dielectric layers and interconnect layers formed on a front side of the substrate. Such a direct incidence makes the BSI image sensor more sensitive to the light.
However, as technologies evolve, the image sensor is becoming increasingly smaller in size while having greater functionality and greater amounts of integrated circuitry. The manufacturing of the BSI image sensor involves many complicated steps and operations. Since more different components with different materials are involved, complexity of the manufacturing and integration operations of the BSI image sensor is increased. An increase in complexity of manufacturing of the BSI image sensor may cause deficiencies such as poor quantum efficiency (QE), dark current, low full well capacity (FWC), high yield loss, etc. The BSI image sensor is produced in an undesired configuration, which would further exacerbate materials wastage and increase the manufacturing cost.
Therefore, there is a continuous need to modify structure and manufacturing method of the BSI image sensor device in order to improve the performance of the BSI image sensor device as well as reduce cost and time on processing the BSI image sensor.